Polyesters have been used as engineering plastics for mechanical parts of various machines, electrical equipment and parts of automobiles. Preferably, engineering plastics are provided with fire-proof or flame retardancy properties in addition to well-balanced physical and chemical properties. Such properties are indispensable in thermoplastic polyesters in order to enlarge their use as engineering plastics, because they are normally used at temperatures higher than 100.degree. C.
Many times flame retarded (FR) glass fiber reinforced (GFR) formulations will drip flaming particles from a molded bar during the UL94 flammability test, especially at the thinner sections of 1/16 or 1/32 inch thickness. This dripping of flaming particles results in a V2 flammability rating instead of the desired V0 rating at a specific thickness.
Flame retarded poly(1,4-cyclohexylenedimethylene terephthalate) (PCT) drips flaming particles at the 1/32 inch thickness during the UL94 flammability test and therefore, only a V2 flammability rating can be obtained at this thickness. Unexpectedly, it has been found that the addition of selected modified polyolefins to PCT will prevent this dripping phenomena and allow V0 flammability ratings at the 1/32 inch thickness.
U.S. Pat. No. 4,879,328 discloses three component polyalkylene terephthalate blends containing selected epoxy compounds with ester linkages and selected elastomers. These are claimed to have improved mechanical properties (impact strength) and stability properties (oven, processing, and hydrolytic properties). This patent does not disclose flame retarded blends or improvements in flammability properties.
Japanese patents 62146948, 62146949, and 62146950 disclose blends of poly(ethylene terephthalate) with glycidyl-containing olefin polymers. These patents do not disclose improved flame resistance, nor do they mention PCT as a polyester component.
Generally speaking, flame retarding agents deteriorate the original physical properties of the base polymer, and therefore it is of importance to find a good combination of polymer and flame retarding agent. In respect to polyesters, several methods have been proposed. The use of antimony oxide in combination with brominated organic compounds is well known in the art of flame retarded polymers. Sodium antimonate used in combination with brominated organic compounds and used as a replacement for antimony oxide to enhance the flame retardancy of poly(ethylene terephthalate) is disclosed in U.S. Pat. No. 4,338,243.
Japanese Patent Publication No. 46-2086 discloses combined use of decabromodiphenyl ether and antimony trioxide as a flame retarding agent. According to this publication, it is possible to reduce the flammability characteristics of glass fiber reinforced polyester resin, but the polyester composition thus obtained is not satisfactory in many physical properties, especially heat deflection temperature, which is essential in certain applications such as electrical circuit boards, etc.
As mentioned above, the use of brominated flame retardants with antimony synergists is well known, and in unreinforced polyester compositions these are effective in extinguishing the flame. The composition still "drips", however, and thus will not attain an acceptable V0 rating in the Underwriters's Laboratories subject 94 test. Unexpectedly, it has been found that the use of certain modified polyolefins improves the flame retardancy of polybutylene terephthalate (PBT) and (PCT).